Liquid crystal display devices have become rapidly popular in place of cathode ray tube (CRT) based display devices in recent years. The liquid crystal display devices have been in widespread use in liquid crystal televisions, monitors, mobile phones, and the like, which take advantage of energy saving, thin, lightweight features and other features of the liquid crystal display devices. One of ways to further take advantage of such features is to improve an illumination device (i.e. a backlight) which is provided behind a liquid crystal display device.
The illumination devices are roughly classified into a side light type (an edge light type) and a direct type. A side light illumination device is arranged so that a light guiding body is provided behind a liquid crystal display panel, and a light source is provided at an edge portion of the light guiding body. Light emitted from the light source is reflected by the light guiding body, so as to illuminate the liquid crystal display panel indirectly and evenly. This allows the illumination device (i) to be thin although low luminance is caused, and (ii) to realize provision of an illumination device superior in brightness uniformity. The side light illumination device therefore has been mainly adopted in small or medium sized liquid crystal display of electronic devices such as a mobile phone or a laptop computer.
An example of the side light illumination device is disclosed in Patent Document 1. Patent Document 1 discloses a surface emission device in which a plurality of dots are formed on a reflecting surface of a light guiding plate so that a light emitting surface emits light uniformly. In this surface emission device, corner regions of the reflecting surface become dark because light does not propagate toward the corner regions due to directivity of the light sources. For this reason, the dots are provided so that their density becomes higher in the corner regions than in the other regions.
A direct illumination device directly illuminates a liquid crystal display panel with the use of a plurality of light sources provided behind the liquid crystal display panel. As such, the direct illumination devices can easily realize high luminance even in a case of a big screen, and therefore have been applied mainly to 20 inch or larger liquid crystal displays. However, an existing direct illumination device is as thick as approximately 20 mm through 40 mm. This prevents the existing direct illumination device from becoming further thinner direct illumination device.
It is possible to realize a much thinner large liquid crystal display by reducing a distance between respective of light sources and a liquid crystal display panel. In this case, however, in order that the illumination device realizes brightness uniformity, it is necessary to increase the number of the light sources. Notwithstanding, an increase in the number of the light sources gives rise to an increase in cost. For this reason, it has been desired to develop a thin illumination device which is superior in brightness uniformity without an increase in the number of the light sources.    [Patent Document 1]    Japanese Unexamined Patent Publication No. 2003-43266 (Tokukai 2003-43266 (published on Feb. 13, 2003))    [Patent Document 2]    Japanese Unexamined Patent Publication No. 288611/1999 (Tokukaihei 11-288611 (published on Oct. 19, 1999))    [Patent Document 3]    Japanese Unexamined Patent Publication No. 82915/1998 (Tokukaihei 10-82915 (published on Mar. 31, 1998))